Venous valves in mammals are usually bicuspid valves, with each cusp forming a sack or reservoir for blood which, under pressure, forces the free edges of the cusps together to prevent retrograde flow of the blood and allow only antegrade flow to the heart. When an incompetent valve attempts to close in response to a pressure gradient across the valve, the cusps do not seal properly and retrograde flow of blood occurs.
There are two chronic venous diseases in which incompetence of venous valves is thought to be an important factor in the pathophysiology. These are varicose veins and chronic deep venous insufficiency.
The varicose vein condition consists of dilatation and tortuously of the superficial veins of the lower limb and resulting cosmetic impairment, pain and ulceration. Primary varicose veins are the result of primary incompetence of the venous valves separating the superficial venous system from the deep venous system. Secondary varicose veins occur as the result of deep venous hypertension which has damaged the valves of the perforating veins.
Chronic deep venous insufficiency consists of deep hypertension of the lower limb with associated pigmentation, pain, swelling, ulceration and varicose veins.
For the sake of convenience, the invention will be described in relation to the correction of incompetent valves in the venous system of the lower limb in man, but, it is to be understood that the invention is not limited thereto.
The venous system of the lower limb consists essentially of the superficial venous system and the deep venous system. The superficial system includes the great saphenous vein and the small saphenous vein. The deep venous system includes the anterior and posterior tibial veins which unite to form the popliteal vein which in turn becomes the femoral vein when joined by the small saphenous vein.
The initial defect in primary varicose veins often involves localized incompetence of a venous valve thus allowing reflux of blood from the deep venous system to the superficial venous system. This incompetence is traditionally thought to arise at the saphenofemoral junction but may also start at the perforators. Thus, gross saphenofemoral valvular dysfunction may be present in even mild varicose veins with competent distal veins. Even in the presence of incompetent perforators, occlusion of the saphenofemoral junction usually normalizes venous pressure.
The initial defect in secondary varicose veins is often incompetence of a venous valve secondary to hypertension in the deep venous system. Since this increased pressure is manifested at many points, correction of one site of incompetence could clearly be insufficient as other sites of incompetence will be prone to develop. Apart from the initial defect, the pathophysiology is similar to that of varicose veins.
Once the initial incompetence occurs, incompetence in other valves in the system will tend to occur secondary to the venous hypertension.
Dilatation of the vein wall, whether idiopathic (primary varicose veins) leads to valvular incompetence. This dilatation may eventually lead to stretching and sclerosis of the valve. Other valves in the system will tend to become incompetent as the reflux of blood causes dilatation of the vein wall. As part of the present invention, it was found that it is possible to reverse or prevent the destructive process by overcoming this dilatation. Even if the vein wall weakness is generalized, as appears to be the case with primary varicose veins, correction of the initial defect will delay or prevent stress being placed no that wall and thus hinder progression of the disease.
Some approaches to restoring competency of incompetent valves have involved venous reconstruction surgery of three basic kinds: venous valve transplants, venous transposition and venous valvuloplasty.
As the term implies, the venous valve transplant approach involves the replacement of the segment of the vein having the incompetent valve with a segment of another vein having a competent valve. The venous transposition approach involves the redirection of the venous system so as to bypass an incompetent valve and venous valvuloplasty involves venous valve reconstructive surgery in which the free length of the valve cusps is reduced by plicating sutures.
These approaches to the prior art are well documented in A Rational Approach to Surgery of the Chronic Venous Stasis Syndrome by Harry Schanzer and E Converse Peirce Annuals of Surgery 1982, 195: 25-29 as well as in Valvuloplasty and Valve Transfer by Seshadri Raju Inter. Angio. 4 1985 419-424.
A single example on one patient of an experimental technique for treating an incompetent venous valve not involving the above types of venous surgery is described in an article by Dag Hallberg in ACTA CHIR SCAND 138: 143-145, 1972. Hallberg placed a band two or three millimeters larger than the diameter of the view around the vein.
The band was made of DACRON™ polyester and polyester and was applied when the patient was in the horizontal position. The band was retained loosely in position by several sutures in the venous adventitia.
Hallberg's method could not restore competence to the majority of the incompetent venous valves. In patients with venous disease, incompetent valves will usually be incompetent in the horizontal as well as the vertical positions. See, for example, Femoral Vein Reconstruction in the Management of Chronic Venous Insufficiency by Ferias Ebb. and Chastener R., ARCHIVES OF SURGERY, 1982, 117:1571-1579.
Ferias and Chastener operated no 53 femoral veins in which the valves had been demonstrated pre-operatively to be incompetent. In only one case was the valve noted to be competent when the patient was horizontal at the time of operation. Chastener's approach was to suture the vein to prevent post-operative dilatation.
It is well known that by itself DACRON™ polyester material causes marked fibrosis as well as foreign body reaction. Therefore, DACRON™ polyester cannot alone be considered biocompatible. In fact, DACRON™ polyester has been employed to stimulate fibrotic reactions which incorporate the synthetic fabric into tissue (see: S. Raju, ANN. SURG. (1983) 197, 688-697).
The article Revasculation of Severely Ischemic Extremities with an Arteriovenous Fistula by F. W. Blaisdell et al. in AMERICAN JOURNAL OF SURGERY, Volume 112, pages 166-173 discloses problems associated with the use of DACRON™ polyester as an implantable material. In a number of cases, gradual narrowing of arteriovenous fistulas under a woven DACRON™ polyester sleeve was demonstrated.
In physical terms, the Hallberg approach was a static one. Once the cuff was sutured into position, no attempt was made to reduce the diameter of the vein at the valve site to restore competency of the valve. Indeed, Hallberg's single patient experiment was concerned with further dilatation of the vein at the valve site rather than reduction in the diameter of the dilated valve to restore competency.
Reference is also made to published PCT application entitled “Correction of Incompetent Venous Valves” (International Application No. PCT/AU87/0021, International Publication No. WO 88/00454), which is incorporated herein by reference.